1. Field of the Invention
The present invention relates to a method of making an electrical contact bump for electrically connecting an electronic microcircuit chip, such as a semiconductor IC chip, to terminal electrodes on a chip support frame.
2. Description of the Prior Art
Soldering has often been used to connect the contacts of an electronic microcircuit chip to conductive terminals on a chip support frame. However, reduction of intervals between the connecting terminals of an electronic microcircuit resulting from recent miniaturization and an increase in the number of the connecting terminals of electronic microcircuits, such as flat package ICs, has made the use of conventional soldering techniques for such purpose difficult. Furthermore, there is a tendency to attach bare IC chips directly to electrodes formed on a glass substrate for the efficient use of a packaging space in electronic desk calculators, electronic watches or liquid crystal displays, which strongly desires effective, precise electrical connecting techniques as a substitute for soldering.
U.S. Pat. No. 4,661,192 discloses a process for electrically bonding a bare IC chip to electrodes on a chip support frame, in which contact bumps are formed on the bonding pads of the IC chip, and the contact bumps are bonded to conductive terminals on a chip support frame by a conductive adhesive to mount the IC chip directly on the chip support frame.
A process for forming such contact bumps on the input and output electrode pads of an IC chip employs a known plating technique. Another process for the same purpose disclosed in U.S. Pat. No. 4,661,192 is a ball bonding process, in which a metallic contact ball is fixed to an electrode pad of an IC chip by a wire bonder, and then the metallic wire is cut off at the neck of the contact ball. A further process disclosed in U.S. Pat. No. 4,442,967 is a ball bonding process, in which a metallic contact ball is fixed to an electrode pad by a wire bonder, the capillary is then moved laterally from the center of the metallic contact ball over a distance 1.5 to two times the diameter of the metallic wire, and then the capillary is lowered to cut off the metallic wire by the lower end of the capillary.
These known ball bonding processes for forming contact bumps are unable to form contact bumps which a height necessary for transferring a conductive adhesive to the IC chip, which is necessary for directly mounting an IC chip on a chip support frame, and in a satisfactorily uniform shape. Furthermore, since the top of the raised contact is flat, the conductive adhesive is spread around the raised contact in mounting the IC chip on the chip support frame which may short-circuit the adjacent terminals, and hence these known ball bonding processes are not applicable to forming of contact bumps at very small intervals. On the other hand, the raised contact forming process employing plating techniques is complex and requires many processing steps and advanced etching and plating techniques. Moreover, the height of the raised contact is limited by the plating accuracy and cost.